1. Field of the Invention
The present invention relates to a measuring method in which whole blood is used as a sample. More particularly, the present invention relates to a method for measuring an analyte contained in a whole blood sample (i.e., a sample comprising whole blood) using an inhibitor of endogenous alkaline phosphatases.
2. Description of the Related Art
An alkaline phosphatase is widely used in labeling an antibody, for example, in an enzyme immunoassay or an enzyme immunostaining. Various alkaline phosphatases widely exist in an animal body. Therefore, when a sample collected from an animal such as a human is used, one or more alkaline phosphatases contained in the sample (hereinafter sometimes referred to as “endogenous alkaline phosphatases”) often affects a result of an enzyme immunoassay or an enzyme immunostaining.
To avoid such an effect, for example, an immunoassay kit using an inhibitor of endogenous alkaline phosphatases [see, for example, Japanese Examined Patent Publication (Kokoku) No. 8-20446], a washing composition comprising an inhibitor of endogenous alkaline phosphatases and a surfactant to reduce a background (see, for example, Japanese Patent No. 3350730), and a method using an inactivated alkaline phosphatase as an absorbent [see, for example, Japanese Unexamined Patent Publication (Kokai) No. 2000-193666] were reported. The term “inhibitor of endogenous alkaline phosphatases” as used herein means an inhibitor which does not inhibit an alkaline phosphatase used as a label but inhibits only endogenous alkaline phosphatases, on the basis of the fact that there are plural alkaline phosphatases having different properties.
In the field of POCT (Point of Care Testing) or the like regarded in a clinical laboratory test, a compact and convenient apparatus or an examining method in which a doctor or a nurse rapidly carry out an examination is desired. A measuring apparatus in which collected whole blood can be used directly without a pretreatment, to accomplish a rapid examination, is desired in the POCT field. If whole blood can be used as a sample, an examination can be carried out more rapidly, those other than an expert can operate the apparatus, and a large apparatus such as a centrifuge is not necessary.
However, when whole blood is used as a sample, the sample contains many interferents, and therefore, an increased background often reduces the accuracy of the measurement, or it is often difficult to measure a small amount of analyte to be analyzed. In particular, the increased background sometimes causes serious problems in a clinical laboratory test, for example, inaccurate measured values or a false decision. No methods to avoid the problems are established. For example, a chemiluminescent immunoassay using an alkaline phosphatase and a sensitive chemiluminescent substrate for the alkaline phosphatase is being developed. When whole blood is used as a sample in such a high-sensitive assay, an extremely increased background reduces the accuracy of the measurement. As factors causing the increased background, for example, an inhibition by one or more interferents, nonspecific binding of interferent protein such as a blood cell membrane, or the like is considered, but the details are unclear. To resolve the problems, a sensitive and high-precision measuring method using a whole blood sample is desired.